Field of the Invention
The subject matter relates to a frame and an axle/suspension system for a heavy-duty vehicle. More particularly, the disclosed subject matter is directed to a pivotal connection between a frame hanger and a beam of the axle/suspension system.
Background Art
Heavy-duty vehicles that transport cargo, for example, tractor-trailers or semi-trailers, and straight trucks such as dump trucks, typically include a leading or trailing arm axle/suspension system that connects an axle of the heavy-duty vehicle to a frame or sub-frame of the heavy-duty vehicle. Although such axle/suspension systems are found in widely varying structural forms, in general their structure is similar in that each axle/suspension system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the axle/suspension systems are connected directly to the primary frame of the heavy-duty vehicle. In other heavy-duty vehicles, the primary frame of the heavy-duty vehicle supports a sub-frame, and the axle/suspension systems connect directly to the sub-frame, which can be non-movable or movable, the latter being commonly referenced to as a slider box, slider sub-frame, slider undercarriage or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to a frame, with the understanding that such reference is by way of example, and that the disclosed subject matter applies to heavy-duty vehicle axle/suspension systems suspended from the longitudinally extending main members of primary frames, movable sub-frames and non-movable sub-frames.
The axle/suspension system is typically suspended from the frame by a pair of aligned and transversely spaced-apart hangers depending from the frame. Each hanger typically includes an outboard wall transversely spaced apart from an inboard wall. The outboard and inboard walls have respective openings and the openings are aligned with one another for providing a pivotal connection between the hanger and respective beam of the respective suspension assembly of the axle/suspension system through a bushing assembly and a fastener group. The hanger may optionally include a front wall which is connected to respective front portions of the outboard and inboard walls so that the hanger has a generally U-shaped horizontal cross-section. Typically, the hanger including only outboard and inboard walls is rigidly mounted to sidewalls of its respective frame main member, whereas the hanger including the front wall in addition to the outboard and inboard sidewalls is rigidly mounted to an underside of its respective frame main member. The fastener group includes bolts, nuts and washers and is used to pivotally connect the bushing assembly to the hanger. The washers may optionally include a concentric member and an eccentric member that enable adjustment of the alignment of the axle/suspension system.
The pivotal connection between the hanger and the beam of the axle/suspension assembly is a location of significant forces including fore-and-aft forces, vertical forces and side forces. This pivotal connection is the only connection between each suspension assembly of the axle/suspension system and the frame of the heavy-duty vehicle, other than an air spring and/or a shock absorber, as are well known. For reacting and/or absorbing the fore-and-aft forces, vertical and side forces, the pivotal connection should include a sufficiently secure clamping engagement between the hanger and the bushing assembly. Typically, the sufficiently secure clamping engagement is formed by aligning hanger openings and a bushing sleeve opening of the bushing assembly and fastening them by inserting a bolt of the fastener group through the openings and tightening the hanger walls against the bushing sleeve. During operation of the vehicle, the beam and its bushing tube can pivot about an elastomeric bushing of the bushing assembly.
In some prior art manufacturing processes, the frame is coated with a protective medium, such as wax to prevent or minimize corrosion and other damage. It has been found that the coated outboard and inboard surfaces of the hanger walls have a relatively low coefficient of friction, thereby inhibiting the secure clamping engagement between the hanger and the bushing assembly, and in turn providing less than an optimal pivotal connection for the suspension assembly to its respective hanger. In order to preserve a desired pivotal connection, contact areas on the outboard and inboard surfaces of each hanger wall must be painted with primer and/or masked off such as with a steel mask and a sealing foam. Such painting and/or masking prevents wax from adhering to that primer-painted and/or masked-off areas of the outboard and inboard surfaces of each hanger wall, thereby preserving better coefficient of friction in the contact areas after assembly of each suspension assembly to its respective hanger. However, the painting-and-masking technique/process is undesirably time-consuming and costly.
In other prior art manufacturing processes, the frame is coated with a protective medium, such as paint to prevent or minimize corrosion and other damage. It has been found that the coated outboard and inboard surfaces of the hanger walls have a relatively low coefficient of friction, thereby inhibiting the secure clamping engagement between the hanger and the bushing assembly, and in turn providing less than an optimal pivotal connection for the suspension assembly to its respective hanger. In order to preserve a desired pivotal connection, a prior art attempt was to use a washer having concentric grooves and a roughened surface on a portion that contacts the hanger. Each groove has a depth from about 1.6 mm (0.063 inch) to about 3.8 mm (0.150 inch). This attempt was found to be insufficient for paint coated hanger walls to provide the sufficient clamping engagement between the hanger and the bushing assembly, and in turn provided less than an optimal pivotal connection for the suspension assembly to its respective hanger.
As a result, there is a need for a structure for a heavy-duty vehicle that enables a frame to be coated with a protective medium but does not require a painting and/or masking process of the hangers that depend from the frame. Thus, undesirable cost and time can be avoided, and a desired pivotal connection is provided between the hanger and the beam of each suspension assembly of the heavy-duty vehicle axle/suspension system. The pivotal connection for suspension assemblies of heavy-duty vehicles of the disclosed subject matter satisfies this need.